Well of course I am very famous *cough*cough* and I'm sure I could find a free window, (maybe the whole of Ever?) if you wanted to cast me!!
(Well, my Grandma was always a big fan!)
I dont really think this is the right place to do this, we could give you and endless list, but we still dont know, how big this show, what sort of size theatre you'd be looking at etc. as there is no point in giving you REALLY famous names, if it's only a small show! and (Please note, I dont understand the production side of shows, I am a mere commoner), but dont BIG shows usually go through Casting Agents for things like this!
"If you talk about my family I will punch you in the fanny so hard it'll end up on your face... oh, looks like someone beat me to it!" - Dawn French